ROD ANCHOR SEAT HAVING SLIDING CLOSURE MEMBER

Abstract: A spinal implant assembly is provided having a top loading anchor (11) which is fixed to a spinal member by a hook (14). The anchor (11) includes a seat member (12) having a channel (22) to receive a stabilizer rod (20) and a sliding interconnecting closure member (16) which slides in a longitudinal direction relative to the seat member (12) to form an integral closed implant assembly. The closure member (16) includes retaining flanges (41) which dovetail relative to undercut retaining flanges (28) of the seat member (12) so as to prohibit the sliding closure member (16) from being dislodged from the seat channel (22), as well as inhibit the splaying of the seat member (12) in response to forces which may be imposed upon the seat member (12) during de-rotation of the spine. In addition, the seat member (12) includes a set screw (18) for locking the rod (20) in position relative to the anchor (11). An instrument (78) is provided which has a spring loaded ball plunger (89) for holding the closure member (16) during assembly to the seat member (12).

Description: ROD ANCHOR SEAT HAVING SLIDING CLOSURE MEMBER FIELD OF INVENTION This invention relates to orthopedic implants, and more particularly to a bone interface anchor for holding a stabilization rod. The anchor can be adjusted after implantation to receive a stabilizer, and is locked into position after assembly. BACKGROUND As surgical techniques have advanced, it has become increasingly common for surgeons to use specially designed hardware for the internal fixation of bones. A particular area of concentration for the recent development of this technology has been the spine. Internal fixation is used most frequently in the spine in conjunction with vertebral fusion, and also for the manipulation of the spine to correct spinal deformities such as scoliosis. There are several important criteria for a hardware system which is used for internal fixation: 1. The implant should provide rigidity as is indicated, generally along the long axis of the patient's spine. 2. The system should be able to accommodate a broad variation in the size and shape of the spinal member with which it is used. For example, the surgeon may wish to use the implant on a variety of individuals. In addition, the difference in the area and size of the point of fixation is compounded by the change in the shape of the vertebrae over the length of the full spinal column. Since it is an advantage to allow the surgeon to master implanting a particular type of aε^ambly, it is preferable if the same or similar anchoring means can be used for a variety of locations. This advantage results in cost efficiency of inventory as well as efficiencies with respect to minimizing the operating time. 3. The hardware must be able to apply and oppose considerable stresses and strains. Thus, the anchor means must be securely fixed to the bone, and the stabilizer must be securely fixed with regard to the anchor means. Moreover, it is desirable to have the integrity to resist breaking. 4. The system should be designed for ease of implantation and removal. Implant hardware is relatively small and therefore somewhat difficult to manipulate. Any difficulty with assembly is compounded by the fact that the assembly occurs during surgery and in a living being. Therefore, it is critical that the hardware is designed with the surgeon's convenience in mind, i.e., to limit the time required and the stress required to implant an assembly. Consequently, a fixation system should be designed to the extent possible for easy assembly while maintaining the option of removal where necessary. SUMMARY OF THE INVENTION The present invention relates to a top- loading rod anchor which has an interlocking sliding member to close the anchor about the rod. The anchor assembly in the present invention includes an anchor having a center slot to allow insertion of the sliding member from the center. The slot includes a lateral undercut which mates with the flanges on the sliding member. Accordingly, it is an object of the present invention to provide a vertebral anchor means which is top-loading, but which converts to a two-piece closed anchor for derotation of the spine. Closed anchor refers to an anchor which at least substantially partially includes the rod so that the anchor means will withstand hoop stresses introduced by manipulating the rod within the anchor. It is a further object of the invention to provide a sliding interconnecting member which cooperates an said anchor seat means by an axially sliding and which has a positive stop which removably locks said sliding member into cooperation with said anchor means. BRIEF DESCRIPTION OF DRAWINGS Figure 1 is an exploded side view of the implant assembly in accordance with the present invention; Figure 2 is an exploded front view of the implant assembly in accordance with the present invention; Figure 3 is a cross-section of the assembled components of Figure 1 taken along line 3-3 of Figure 2; Figure 4 is a cross-section of the assembled components taken along line 4-4 of Figure 1; Figure 5 is a top view of the sliding interlocking seat closure member as shown in Figure 1; Figure 6 is a cross-section of the closure member taken along line 6-6 of Figure 5; Figure 7 is a cross-section of the sliding member taken along line 7-7 of Figure 5; and Figure 8 is a top plan view of the anchor used with the implant assembly of Figure 1; Figure 9 is a side cross-sectional view taken along line 9-9 of the anchor of Figure 8; Figure 10 is a front cross-sectional view taken along line 10-10 of the anchor of Figure 8; and Figure 11 is an instrument for the alignment and implantation of the sliding interconnecting rod closure member as shown in Figures 1-4. DETAILED DESCRIPTION OF THE INVENTION Figure 1 illustrates an exploded side view of the spinal implant assembly of the present invention. The implant assembly 10 comprises a stabilization means, i.e., rod 20, and an implant anchor 11. The anchor includes a seat 12 which is fixed to the spine by fixation means, in this case, a hook 14. However, the invention could also be practiced with other fixation means such as a bone screw. The seat 12 includes a recess 23 which receives the rod about its longitudinal axis and which is loaded from the top of the seat. The seat is closed by a sliding interconnecting closure member 16 which has a sliding interlocking engagement with seat member 12. More specifically, the closure member 16 is dropped into an engagement on the rod 20 and slid in a direction along the rods' longitudinal axis so as to form an interlocking engagement with the seat 12. A set screw 18 cooperates with the closure member to apply a compressive force on the rod and secure the rod relative to the seat member. The seat 12 includes a channel 22 which has in its bottom a rod recess 23 which is contoured to accept the rod 20. Optionally, the rod recess 23 may include a surface interface so as to increase the compressive interface between the rod 20 and the seat, such as interrupted serrations. The channel 22 includes in its upper portion a recess 26 which is formed on the inside of a seat shoulder 27. In addition, the flange members 28 which form the seat shoulder 27 include a slight protuberance 29 which mates with grooves 30 on the closure member 16 to bias the closure member 16 into position with regard to the seat member 12. The seat member includes a cutouts 43 in the flange members 28 which enables the sliding closure member 16 to be loaded into the seat 12 from a central position with a small sliding movement, in contrast to sliding the closure member along the entire length of the channel 22 from either direction. The anchor 11 also includes a closure member 16 which acts with the seat 12 to present a closed anchor 11 which facilitates the manipulation and specifically, the derotation of the spine. Since the closure member has a dove-tailed relationship with the seat member 12 to allow a sliding interlocking engagement. The seat member 12 may be loaded from the top with the rod 20 and subsequently closed with the closure member 16 so as to fix the rod relative to the fixation means, but to allow rotation of the rod about its longitudinal axis. The closure member 16 includes projecting flanges 41 which have include a recess 39 on their upper surface, and a sliding shoulder 40 outward from the recess 39. The shoulders 40 of the closure member 16 form a dove-tailed cooperation with the shoulders 27 of the seat member, which cooperation inhibits the sliding closure member from being pulled out of the channel 22 of the seat member 12, and further which inhibits the sides 53, 54 of the seat member which form the channel 22 from splaying in response to a rotational force applied to the rod and cap member, respectively. The closure member further includes a curved or arched rod interface surface 37 which mates with the top surface of the rod 20. The closure member 16 includes a hole 33 which is threaded with internal threads 34 to receive a set screw 18 having external threads 19. Thus, the set screw 18 can be screwed down relative to the closure member 16 to form a compressive interface with the rod 20. It is a further advantage that the set screw 18 includes a bevel 47 having serrations 48 and a countersink 49 to inhibit the stripping of the set screw and seat threads, as well as improve the compressive grip of the set screw on the rod 20. In addition, the sliding member has opposing cutout sections 42 corresponding to the cutout section 43 of the seat member to facilitate an intermediate loading of the sliding closure member 16 relative to the seat 12. The seat member 12 has multiple grooves 30 which receive the protuberance 29 of the seat to cause a friction lock between the closure member and the seat member, which lock can be overcome by sliding the closure member along the longitudinal axis of the rod. The closure member has opposing retaining dimples on its front and rear surface which facilitate the assembly of the closure member relative to the seat using an instrument 78 shown in Figure 8 of the present application. In addition, the set screw has a hex opening 46 to allow the set screw to be driven into engagement with the rod 20 using a hex driver. An instrument 78 is shown for assembly of the closure member relative to the seat member and includes a handle 80 an 82 shaft of a length appropriate to allow the surgeon access to the implant, and a pronged instrument head 84. The head 84 includes an opening 86 of a size appropriate to receive the closure member 16, which opening 86 is defined first and second arms 85. The first and second arms respectively include a boss 88 and a spring loaded plunger ball 89. The ball is held in engagement relative to the closure member 16 by biasing means 90. While in accordance with the Patent Statutes, the best mode and preferred embodiment has been set forth, the scope of the invention is not limited thereto, but rather by the scope of the attached claims.

Claims: WHAT IS CLAIMED IS: 1. A retaining member for use with an elongated stabilizer for a spine, said holding means comprising: a seat having a channel, said channel having an axis in a first direction, said channel receiving said elongated stabilizer so that the longitudinal axis of said stabilizer is aligned in said first direction, and a sliding closure member, said closure member having a sliding cooperation with said seat whereby said closure member may be slid in the first direction to engage said seat, and said seat including means to retain said closure member from disengagement from said channel. 2. A retaining member as set forth in claim 1, wherein said anchor closure member includes a rod interface surface which cooperates with less than all of the circumference of said rod. 3. An member as set forth in claim 2, wherein said closure member has a rod interface surface which extends through a range of less than about 270 degrees. 4. A member as set forth in claim 1, wherein said closure member has a dove-tailed cooperation with said seat. 5. A member as set forth in claim 4, wherein said seat includes first and second seat mating shoulders and said dove tail includes first and second mating shoulder members which mate with the seat mating shoulders inhibit the splaying of said seat means. 6. A member as set forth in claim 1, wherein said seat means includes a central opening to allow said sliding closure means to be engaged with said seat by loading said closure member through said opening and sliding it into a locked engagement. 7. An anchor member as set forth in claim 1, wherein said retaining means includes an interlocking biasing friction fit. 8. An anchor means for use with a stabilizer rod comprising a seat having a channel, said channel having a rod receiving recess and being open outwardly of said recess, said channel including a first sidewall and a second sidewall, said first and said second sidewalls terminating in opposing flanges; and a sliding slide closure member having a rod receiving arch and including flanges which mate with said seat flanges to form a closed rod receiving channel. 9. An anchor means as set forth in claim 8, wherein said closure member includes a threaded bore substantially perpendicular to the longitudinal axis of said channel and said anchor means further includes at least one set screw received in said bore. 10. An anchor as set forth in claim 9, wherein said set screw includes a rod contacting terminus having a high friction surface. 11. An anchor as set forth in claim 8, wherein said mating flanges include means to inhibit splaying of said first and said second sidewalls. 12. An instrument for use with an anchor member, said anchor member securing an elongated stabilizer relative to a spine, and said anchor member having a channel to receive said stabilizer and a sliding closure means having a sliding cooperation with said seat means whereby said sliding closure means may be slid in the direction of the longitudinal axis of said stabilizer to engage said seat means, said instrument comprising a handle portion, a shaft portion, and a head portion, said head portion receiving said closure means and having a biased releasable engagement with said closure means. 13. An instrument as set forth in claim 9, wherein said biased releasable engagement is provided by a spring loaded ball plunger.

Inventors: BYRD J ABBOTT III, MELLINGER PHILIP A, PUNO ROLANDO M, BYRD, J., ABBOTT, III, MELLINGER, PHILIP, A., PUNO, ROLANDO, M.
Applicants: CROSS MED PROD INC, CROSS MEDICAL PRODUCTS, INC.
Application year: 1994
Main classification: A61B17
IPC codes: A61B17